Abstract

​Increasing the energy and power density of lithium ion batteries (LIBs) is required to reduce the cost and increase the range of hybrid/electric vehicles. One strategy is to reduce the amount of non-capacitive materials in the cathode, such as the polymer binder or conductive additive, by replacing traditional carbon black with single walled carbon nanotubes (SWNTs). The advantages of nanotubes are that they are more conductive, have high aspect ratio, have excellent mechanical properties and have good chemical stability. The high conductivity and aspect ratio of SWNTs leads to a composite material that achieves percolation with less conductive additive needed. In addition, the SWNTs provide an electrochemically stable scaffold for the cathode active material that can accommodate changes during battery cycling. Therefore, the SWNTs should improve gravimetric capacity by eliminating the need for binder, reducing the amount of conductive additive needed, and should improve rate performance and cycle stability.

Despite the advantages SWNTs provide in LIB cathodes, current techniques (ball milling; mixing/sonication/vacuum filtration) are limited by SWNT agglomeration and are not easily scalable. To overcome these limitations, we show that it is possible to create binder-free and flexible LIB cathodes by direct gas phase mixing of SWNTs grown in a liquid injection chemical vapor deposition reactor with an aerosol of cathode active material, LiNiCoMnO2 (LNMC or NMC). This technique shows promise for scalability because it minimizes agglomeration of SWNTs while eliminating most post-mixing processing. Both coin cell and laminate cell battery testing were performed on these cathode composite materials to investigate their suitability for use in light weight and high power lithium ion batteries.